In recent years, numerical control of machine tools has made remarkable progress, and made possible various improvements in machine tools such as automation thereof, improvement in productivity, reduction in machine cost and so forth.
In comparison with conventional universal machine tools in general however, machine tools which may be provided with numerical control are typically extremely costly. In addition, universal machine tools have retained a predominance in this field of art. For these reasons, attempts have been made to automate universal machine tools in use by modifying them to provide them with numerical control. Yet these attempts have mostly failed to provide a really satisfactory result. The principal difficulty with the conventional method has been the object positioning system. This is a serious problem because said positioning system of the object is of utmost importance for performing the numerical control satisfactorily.
In other words, a typical system of positioning for numerical control employs a pulse motor as a driving source of the object to be controlled whereby a distance of movement of the object to be controlled is converted to an angle of revolution of the pulse motor so that positioning of the object may be controlled by means of an instruction code punched on a tape related to quantity, speed, direction, etc. of revolution of the pulse motor.
The above-described positioning system likewise calls essentially for high precision feed screws as well as bearing means in order to accurately transmit the quantity and speed of revolution of the pulse motor to the object to be controlled. Needless to say, these component parts are extremely expensive. Further, to reduce aging of a sliding part of the machine tool and enhance rigidness thereof, quenching or similar processing must be performed to assure high rigidity in the sliding part, resulting in further increase in the cost of production.
Moreover, programming of the tape for the control of the pulse motor requires essentially much skill and a long period of time. Taken together with the above-mentioned problems, this further increases the cost of production.
When universal machine tools are modified to employ a positioning system including a pulse motor so that numerical control may be utilized, various parts of the machine tools, e.g., driving section, must be modified. The cost benefit of the numerical control oftentimes does not balance with the cost of modification. This imposes one of the major obstacles to the wide use of numerical control in the field of the machine tools.
The primary object of the present invention is, therefore, directed to provide an automatic positioning apparatus for use in the numerical control of machine tools and other machines which makes it possible to effect positioning of the moving part of the machines with high accuracy.
It is another object of the present invention to provide an automatic positioning apparatus for use in the numerical control of universal machine tools which are already in use, without substantial modification thereof, said apparatus being capable of insuring highly accurate positioning of the moving part.
Still another object of the present invention is to inexpensively provide the above-described automatic positioning apparatus.
These and other objects and features of the invention will become apparent from the claims and from the following description when read in conjunction with the appended drawings.